I understand for safety about backing off... but where powder is impossible to find and also bullets, it maybe easier to just wait for the primers I have always used rather than working up the ladder test lol. A year ago I never would have second guesses going out and trying to perfect the load. Now days it seems I hope for lass than 1" groups and call it good just so im not dumping precious resources away

As explained in Barnes Univ.; if you are throwing loads over 60 or so grains you will get a more efficient powder burn with a magnum primer, therefore more velocity because you burned more powder in the cartridge case.

Put another way; The more powder you can burn in the cartridge case the more gas pressure will be created and the more velocity you will generate.

This is why WSM cartridges generate the same velocities with 12% less powder.

The powder is strung out the length of the cartridge case as it lays parallel to the earth (like on a shooting bench). The longer the "line" of powder, the longer it takes to burn. Once the gas pressure is sufficient to pop the bullet out of the crimp, the burn rate of the remaining powder drops big time. There are some interesting test result on the web showing this relationship.

Take a 300 WSM cartridge and a 300 win mag cartridge and lay them on a table. Its easy to understand that the powder in the 300WM would take longer to burn than a 300WSM due to the length of the "line" of powder, even though we are talking mili sec.

Something I've found too be true (from fiddling with muzzleloaders and changing the physical attributes between the primer itself and the breechplug face) is that different brands of primers are actually different overall lenghts and vary by a couple thousands between brands.

This becomes especially critical when reducing the breechplug face to firing pin retainer clearance in an inline muzzleloader to reduce primer blowby and increase powder burn. Get to too tight (too little clearance and you get a slam fire when closing the action or change brands of primers and a taller primer causes the same scenario.

Which is why I stick with one brand (CCI). Cup diameter also varies a bit from brand to brand but the diameter varience is much less than overall height. Cup diameters vary a couple 10ths.

I've heard that one should always seat primers to the bottom of the pocket but I only seat my primers (in cartridges) flush with the casehead and no more. As widely proven, primers that are proud of the casehead can cause slam fires and rule of thumb is 1-2 thousands below the casehead, but again, I seat level with the casehead.

At least in my perspective, sticking with one brand and quality (benchrest, magnum or regular) goes a long way towatd shot after shot repetability.

I realize that with the component availability being what it is, that may not be practical but I would strongly suggest working up the load again, if you change brands of primers or the quality in the same brand.